THz instruments are being proposed as highly sensitive instruments for the remote sensing of planetary atmospheres on Mars, Venus, Jupiter, Saturn and Saturn's moon Titan. For these long-term planetary missions, severe constraints are put on the mass and power budget for the payload instruments. See for example V. M. Lubecke, K. Mizuno, G. M. Rebeiz, “Micromachining for terahertz applications”, IEEE-MTT, pp. 1821-1831, 1998. Conventional approaches which package the receiver components in CNC machined metal waveguide blocks are too massive and expensive for multi-pixel instruments that fit within these tight budgets.
Several different micromachining techniques exist for fabrication of terahertz circuits. One process forms the waveguide and device structures directly from permanent resists such as SU-8, as is described in J. Stanec and N. Barker, “Fabrication and integration of micromachined submillimeter-wave circuits,” Microwave and Wireless Components Letters, IEEE, vol. 21, no. 8, pp. 409-411, August 2011. This technique, while requiring a minimum of processing tools, suffers from significant process instabilities and delamination issues between the thick resist and carrier wafer.
LIGA-based processes use thick resists to form a mold for electroplating, as described in C. H. Smith, H. Xu, and N. Barker, “Development of a multilayer SU-8 process for terahertz frequency waveguide blocks,” Microwave Symposium Digest, 2005 IEEE MTT-S International, pp. 439-442, June 2005. This has the advantage of producing a metal structure and is therefore easier to couple to standard metal waveguide components. However, both of these processes suffer from non-uniformity issues that require an additional processing step, such as lapping, to planarize the final device.
There is a need for ultra-compact receiver architectures to reduce the mass and size of the receiver while increasing the circuit density of the device.
There is a need for fabrication methods that will permit the accurate fabrication of such devices in silicon.